Photomask and manufacturing method thereof

ABSTRACT

A method of manufacturing a photomask includes at least the following steps. First, a phase shift layer and a hard mask layer are formed on a light transmitting substrate. A predetermined mask pattern is split into a first pattern and a second pattern. A series of processes is performed so that the hard mask layer and the phase shift layer have the first pattern and the second pattern. The series of processes includes at least the following steps. First, a first exposure process for transferring the first pattern is performed. Thereafter, a second exposure process for transferring the second pattern is performed. The first exposure process and the second exposure process are executed by different machines.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of U.S. provisionalapplication Ser. No. 62/512,738, filed on May 31, 2017. The entirety ofthe above-mentioned patent application is hereby incorporated byreference herein and made a part of this specification.

BACKGROUND

Photolithography is utilized in the fabrication of semiconductor devicesto transfer a pattern onto a wafer. Based on various integrated circuit(IC) layouts, patterns are transferred from a photomask (or a reticles)to a surface of the wafer. As dimensions decrease and density in ICchips increases, resolution enhancement techniques, such as opticalproximity correction (OPC), off-axis illumination (OAT), double dipolelithography (DDL) and phase-shift mask (PSM), are developed to improvedepth of focus (DOF) and therefore to achieve a better pattern transferonto the wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A-1L are schematic cross-sectional views illustrating a processflow for manufacturing a photomask in accordance with some embodimentsof the disclosure.

FIGS. 2A-2O are schematic cross-sectional views illustrating a processflow for manufacturing a photomask in accordance with some alternativeembodiments of the disclosure.

FIGS. 3A-3G are schematic cross-sectional views illustrating a processflow for manufacturing a photomask in accordance with some alternativeembodiments of the disclosure.

FIGS. 4A-4K are schematic cross-sectional views illustrating a processflow for manufacturing a photomask in accordance with some alternativeembodiments of the disclosure.

FIG. 5A is a schematic top view illustrating a first mask layer duringthe first exposure process in FIG. 3A.

FIG. 5B is a schematic top view illustrating a first mask layer duringthe second exposure process in FIG. 3B.

FIG. 5C is a schematic top view illustrating a portion of a photomask.

FIG. 6 is a schematic top view illustrating a first mask layer in FIG.3A in accordance with some alternative embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The advanced lithography process, method, and materials described in thecurrent disclosure can be used in many applications, including fin-typefield effect transistors (FinFETs). For example, the fins may bepatterned to produce a relatively close spacing between features, forwhich the above disclosure is well suited. In addition, spacers used informing fins of FinFETs can be processed according to the abovedisclosure.

FIGS. 1A-1L are schematic cross-sectional views illustrating a processflow for manufacturing a photomask 10A in accordance with someembodiments of the disclosure. Referring to FIG. 1A, a lighttransmitting substrate 100 is provided. A phase shift layer 200 and ahard mask layer 300 are sequentially formed on the light transmittingsubstrate 100. In other words, the phase shift layer 200 is sandwichedbetween the hard mask layer 300 and the light transmitting substrate100. A first mask layer 400 is formed on the hard mask layer 300. Insome embodiments, the structure illustrated in FIG. 1A is split into afirst block B1 and a second block B2. The configurations of the firstblock B1 and the second block B2 will be discussed in greater detaillater.

In some embodiments, the light transmitting substrate 100 may be formedof quartz glass, synthetic quartz glass, or fluorine-doped quartz glass.In some embodiments, the light transmitting substrate 100 is deemedtransparent under near ultra violet (NUV) wavelengths (e.g., less than365 nanometers (nm)). In some embodiments, the light transmittingsubstrate 100 is deemed transparent under deep ultra violet (DUV)wavelengths (e.g., less than 248 nm). In some embodiments, the lighttransmitting substrate 100 is deemed transparent under argon fluoride(ArF) laser (e.g., 193 nm).

In some embodiment, a material of the phase shift layer 200 includeschromium, chromium oxide, chromium oxynitride or another suitablematerial; a MoSi compound; or the like. The MoSi compound, for example,includes at least one among MoSi, MoSiCON, MoSiON, MoSiCN, MoSiCO,MoSiO, MoSiC, and MoSiN. As illustrated in FIG. 1A, the phase shiftlayer 200 is directly disposed on the light transmitting substrate 100and immediately underneath the hard mask layer 300. However, thedisclosure is not limited thereto. In some alternative embodiments,additional layer may be presented between the light transmittingsubstrate 100 and the phase shift layer 200 and/or between the phaseshift layer 200 and the hard mask layer 300. In some embodiments, thephase shift layer 200 may be formed by a deposition process (such aschemical vapor deposition (CVD), physical vapor deposition (PVD), oratomic layer deposition (ALD)), a sputter method, or the like.

In some embodiments, the hard mask layer 300 is an opaque layer. Amaterial of the hard mask layer 300 may include metals, metal oxides, orother suitable materials. For example, the hard masks layer 300 may bemade of chrome (Cr), chrome oxide, chromium oxynitride, or anothersuitable material. The material of the hard mask layer 300 is notlimited herein as long as such material is able to block incident light.Similar to the phase shift layer 200, in some embodiments, the hard masklayer 300 may also be formed through a deposition process (such as CVD,PVD, or ALD), a sputter method, or the like.

In some embodiments, the first mask layer 400 is utilized to pattern theunderlying hard mask layer 300 in the subsequent processes. That is, thefirst mask layer 400 may be a photoresist layer. In some embodiments,the first mask layer 400 may be a chemically amplified resist thatemploys acid catalysis. For example, the first mask layer 400 may beformulated by dissolving an acid sensitive polymer in a castingsolution. In some embodiments, the first mask layer 400 may be apositive tone photoresist which would render the patterns subsequentlyformed having the same contour as the patterns on a mask (notillustrated). In some alternative embodiments, the photoresist layer maybe a negative tone photoresist which would render the patternssubsequently formed having openings corresponding to the patterns on themask (not illustrated).

Referring to FIG. 1A, a first exposure process is performed on the firstmask layer 400. In some embodiments, the first exposure process mayinclude a lithography technique with a mask (for instance, aphotolithography process) or a mask-less lithography technique (forinstance, an electron-beam (e-beam) exposure process or an ion-beamexposure process). In some embodiments, the first exposure process isperformed by irradiating a light beam onto at least a portion of thefirst mask layer 400 to form an exposure region 402. In someembodiments, the exposure region 402 is located in the first block B1.In other words, the first exposure process is performed within the firstblock B1.

Referring to FIGS. 1A and 1B, after the first exposure process, apost-baking process may be performed to harden at least a portion of thefirst mask layer 400. Depending on the material(s) or type(s) of thefirst mask layer 400, polymers of the first mask layer 400 may undergodifferent reactions (chain scission or cross-linking of polymers) uponthe irradiation of the light beam and baking. Thereafter, a firstdevelopment process is performed to remove at least a portion of thefirst mask layer 400. In some embodiments, portions of the positiveresist material exposed to the light beam may undergo chain scissionreaction, resulting the exposed portions to be easily removed by adevelopment agent as compared to other portions not exposed to the lightbeam. On the other hand, portions of the negative resist materialexposed to the light beam may undergo the cross-linking reaction,resulting the exposed portions to be harder to remove by a developmentagent as compared to other portions not exposed to the light beam. Insome embodiments, the first mask layer 400 is made of positive toneresist material, so the exposure region 402 is subjected to the chainscission reaction. Referring to FIG. 1B, the exposure region 402 isremoved such that the first pattern P1 of the mask (not illustrated) istransferred onto the pattern first mask layer 400 a. In someembodiments, the first pattern P1 of the patterned first mask layer 400a exposes at least a portion of the underlying hard mask layer 300.

Referring to FIGS. 1B and 1C, a first etching process is performed totransfer the first pattern P1 onto the patterned hard mask layer 300 a.For example, during the first etching process, the patterned first masklayer 400 a may be adapted as a mask such that portions of the hard masklayer 300 exposed by the first pattern P1 is removed to render thepatterned hard mask layer 300 a having the first pattern P1. In someembodiments, the first etching process may be a selective etchingprocess. In some embodiments, the first etching process may include adry etching process, a wet etching process, or a combination thereof. Insome embodiments, the first pattern P1 of the patterned hard mask layer300 a exposes at least a portion of the underlying phase shift layer200.

Referring to FIGS. 1C and 1D, the patterned first mask layer 400 a isremoved. The patterned first mask layer 400 a may be removed through,for example, a resist stripping process or a resist ashing process.After the patterned first mask layer 400 a is removed, the structureillustrated in FIG. 1D may further undergo a first inspection (afterstripping inspection, ASI) process and a cleaning process. During thefirst inspection process, the first pattern P1 is inspected to ensurethat the contour of the first pattern P1 is in accordance with thedesired pattern (the pattern of the mask provided initially).

Referring to FIGS. 1D and 1E, an additional etching process is performedto transfer the first pattern P1 onto the patterned phase shift layer200 a. For example, during the additional etching process, the patternedhard mask layer 300 a may be adapted as a mask such that portions of thephase shift layer 200 exposed by the first pattern P1 is removed torender the patterned phase shift layer 200 a having the first patternP1. Since the first pattern P1 of the patterned phase shift layer 200 ais formed by adapting the patterned hard mask layer 300 a as the mask,the contour of the first pattern P1 in the patterned phase shift layer200 a and the contour of the first pattern P1 in the patterned hard masklayer 300 a are substantially identical and are aligned. In someembodiments, the additional etching process may include a dry etchingprocess, a wet etching process, or a combination thereof. It should benoted that due to the material difference between the hard mask layer300 and the phase shift layer 200, the etching recipe of the firstetching process and the additional etching process may be different. Insome embodiments, the steps illustrated in FIGS. 1A-1E may becollectively referred to as a first patterning process.

Referring to FIG. 1F, a second mask layer 500 is formed on the patternedhard mask layer 300 a. A material and a formation method of the secondmask layer 500 may be similar to the first mask layer 400, so thedetailed description thereof is omitted herein.

Referring to FIG. 1G, a second exposure process is performed on thesecond mask layer 500. The second exposure process may be similar to thefirst exposure process, so the detailed description thereof is omittedherein. In some embodiments, the second exposure process is performed byirradiating a light beam onto at least a portion of the second masklayer 500 to form an exposure region 502. In some embodiments, theexposure region 502 is located in the second block B2. In other words,the second exposure process is performed within the second block B2. Insome embodiments, since the precision requirements of the patterns inthe first block B1 and the second block B2 are different, the firstexposure process and the second exposure process may be executed bydifferent machines. For example, in some embodiments, if the patterns inthe first block B1 require higher precision (having dense pitch orfeature size) than the patterns in the second block B2, the firstexposure process may be executed by a machine with higher resolution(advanced machine) while the second exposure process may be executed bya machine with lower resolution (lower grade machine). In somealternative embodiments, if the patterns in the first block B1 requirelower precision than the patterns in the second block B2, the firstexposure process may be executed by a machine with lower resolutionwhile the second exposure process may be executed by a machine withhigher resolution. As such, different machines may be fully utilized toreduce the manufacturing time by 8%-20%, thereby increasing thethroughput of the photomask. Examples of the patterns requiring lowerprecision include dummy pattern, trivial pattern, or the like. It shouldbe noted that the foregoing procedure adapted lithography technique witha mask as an example, but the disclosure is not limited thereto. In acase where mask-less lithography technique is adapted, different writersmay be utilized to form the patterns in the first block B1 and thepatterns in the second block B2.

Referring to FIGS. 1G and 1H, a second development process is performedto remove at least a portion of the second mask layer 500. In someembodiments, the exposure region 502 is removed such that the secondpattern P2 of the mask (not illustrated) is transferred onto the patternsecond mask layer 500 a. In some embodiments, the second pattern P2 ofthe patterned second mask layer 500 a exposes at least a portion of theunderlying patterned hard mask layer 300 a.

Referring to FIGS. 1H and 1I, a second etching process is performed totransfer the second pattern P2 onto the patterned hard mask layer 300 b.For example, during the second etching process, the patterned secondmask layer 500 a may be adapted as a mask such that portions of thepatterned hard mask layer 300 a exposed by the second pattern P2 isremoved to render the patterned hard mask layer 300 b having the secondpattern P2. In some embodiments, the second etching process may includea dry etching process, a wet etching process, or a combination thereof.In some embodiments, the recipe of the second etching process may beidentical to the first etching process. In some alternative embodiments,the second etching process may be different from the first etchingprocess. In some embodiments, the second pattern P2 of the patternedhard mask layer 300 b exposes at least a portion of the underlyingpatterned phase shift layer 200 a.

Referring to FIGS. 1I and 1J, a third etching process is performed totransfer the second pattern P2 onto the patterned phase shift layer 200b. For example, during the third etching process, the patterned secondmask layer 500 a and the patterned hard mask layer 300 b may be adaptedas masks such that portions of the patterned phase shift layer 200 aexposed by the second pattern P2 is removed to render the patternedphase shift layer 200 b having the second pattern P2. Since the secondpattern P2 of the patterned phase shift layer 200 b is formed byadapting the patterned hard mask layer 300 b as the mask, the contour ofthe second pattern P2 in the patterned phase shift layer 200 b and thecontour of the second pattern P2 in the patterned hard mask layer 300 bare substantially identical and are aligned. In some embodiments, thethird etching process may include a dry etching process, a wet etchingprocess, or a combination thereof. It should be noted that due to thematerial difference between the hard mask layer 300 and the phase shiftlayer 200, the etching recipe of the second etching process and thethird etching process may be different. In some embodiments, the recipeof the third etching process may be identical to the first etchingprocess and/or the additional etching process. In some alternativeembodiments, the third etching process may be different from the firstetching process or the additional etching process.

Referring to FIGS. 1J and 1K, the patterned second mask layer 500 a isremoved. The patterned second mask layer 500 a may be removed through,for example, a resist stripping process or a resist ashing process.After the patterned second mask layer 500 a is removed, the structureillustrated in FIG. 1K may further undergo a cleaning process. In someembodiments, the steps illustrated in FIGS. 1F-1K may be collectivelyreferred to as a second patterning process.

Referring to FIGS. 1K and 1L, the patterned hard mask layer 300 b isremoved to obtain the photomask 10A. As illustrated in FIG. 1L, afterthe patterned hard mask layer 300 b is removed, regions of the lighttransmitting substrate 100 corresponding to the first pattern P1 and thesecond pattern P2 are exposed by the patterned phase shift layer 200 b.The photomask 10A has a predetermined mask pattern P which is split intoa first pattern P1 and a second pattern P2. The first pattern P1 islocated in the first block B1 and the second pattern P2 is located inthe second block B2. In some embodiments, after the patterned hard masklayer 300 b is removed, the photomask 10A may be subject to a secondinspection process. During the second inspection process, the secondpattern P2 is inspected to ensure that the contour of the second patternP2 is in accordance with the desired pattern (the pattern of the maskprovided initially). As mentioned above, the first pattern P1 and thesecond pattern P2 may be formed by different machines due to thedifference in precision requirements. Similarly, in some embodiments,the first inspection process and the second inspection process may beperformed by inspection machines with different precisions.

In some embodiments, the photomask 10A may be referred to as a superbinary mask (SBIM). The SBIM includes the light transmitting substrate100 and the patterned phase shift layer 200 b. During thephotolithography process, patterns are transferred to a surface of awafer by transmitting light through the light transmitting substrate anda small percentage of light incident on the phase shift layer propagatesthrough the patterned phase shift layer 200 b, to selectively expose aphotomask layer on a wafer. In some embodiments, from about 6% to about9% of incident light propagates through the patterned phase shift layer200 b. In some other embodiments, about 12% of incident light propagatesthrough the patterned phase shift layer 200 b. Further, the patternedphase shift layer 200 b is used to shift a phase of selected lightpassing through the mask or the reticle by π (180 degrees), thereby theundesired light is offset by the destructive interference. Removing theundesired light helps to improve the precision of the image transfer. Insome embodiments where the mask is a super binary mask, a thickness ofthe patterned phase shift layer 200 b is greater than 40 nm. However,one of ordinary skill in the art would understand that the thickness ofthe opaque layer is determined by a transmission rate of the selectedmaterial and a depth of focus (DOF) during the process.

FIGS. 2A-2O are schematic cross-sectional views illustrating a processflow for manufacturing a photomask 10B in accordance with somealternative embodiments of the disclosure. Referring to FIGS. 2A-2F, thesteps described herein is similar to the steps of FIGS. 1A-1F, so thedetailed description thereof is omitted herein.

Referring to FIG. 2G, a second exposure process is performed on thesecond mask layer 500. The second exposure process may be similar to thefirst exposure process, so the detailed description thereof is omittedherein. In some embodiments, the second exposure process is performed byirradiating a light beam onto at least a portion of the second masklayer 500 to form an exposure region 502 and an exposure region 504. Insome embodiments, the exposure region 502 is located in the first blockB1 and the exposure region 504 is located in the second block B2. Inother words, the second exposure process is performed on both of thefirst block B1 and the second block B2. In some embodiments, theexposure region 502 is formed to be partially overlapped with the firstpattern P1.

Referring to FIGS. 2G and 2H, a second development process is performedto remove at least a portion of the second mask layer 500. In someembodiments, the exposure region 502 and the exposure region 504 areremoved such that the third pattern P3 and the second pattern P2 of themask (not illustrated) are respectively transferred onto the patternsecond mask layer 500 a. In some embodiments, the second pattern P2 andthe third pattern P3 of the patterned second mask layer 500 a exposes atleast a portion of the underlying patterned hard mask layer 300 a. Insome embodiments, the third pattern P3 of the patterned second masklayer 500 a is partially overlap with the first pattern P1. In otherwords, the third pattern P3 also exposes the first pattern P1.

Referring to FIGS. 2H and 2I, a second etching process is performed totransfer the second pattern P2 and the third pattern P3 onto thepatterned hard mask layer 300 b. For example, during the second etchingprocess, the patterned second mask layer 500 a may be adapted as a masksuch that portions of the patterned hard mask layer 300 a exposed by thesecond pattern P2 and the third pattern P3 is removed to render thepatterned hard mask layer 300 b having the second pattern P2 and thethird pattern P3. In some embodiments, the recipe of the second etchingprocess may be identical to the first etching process. In somealternative embodiments, the second etching process may be differentfrom the first etching process. In some embodiments, the second patternP2 and the third pattern P3 of the patterned hard mask layer 300 bexpose at least a portion of the underlying patterned phase shift layer200 a. In addition, the third pattern P3 also exposes the first patternP1.

Referring to FIGS. 2I and 2J, the patterned second mask layer 500 a isremoved. The patterned second mask layer 500 a may be removed through,for example, a resist stripping process or a resist ashing process.After the patterned second mask layer 500 a is removed, the structureillustrated in FIG. 2J may further undergo a cleaning process. In someembodiments, the steps illustrated in FIGS. 2F-2J may be collectivelyreferred to as a second patterning process.

Referring to FIG. 2K, a third mask layer 600 is formed on the patternedhard mask layer 300 b. A material and a formation method of the thirdmask layer 600 may be similar to the first mask layer 400 and the secondmask layer 500, so the detailed description thereof is omitted herein.

Referring to FIG. 2L, a third exposure process is performed on the thirdmask layer 600. The third exposure process may be similar to the firstexposure process and the second exposure process, so the detaileddescription thereof is omitted herein. In some embodiments, the thirdexposure process is performed by irradiating a light beam onto at leasta portion of the third mask layer 600 to form an exposure region 602. Insome embodiments, the exposure region 602 is located in the second blockB2. For example, the exposure region 602 may be aligned with the secondpattern P2 of the patterned hard mask layer 300 b. In other words, thethird exposure process is performed within the second block B2. In someembodiments, the first exposure process, the second exposure process,and the third exposure process may be executed by different machines.However, the disclosure is not limited thereto. In some alternativeembodiments, the first exposure process and the third exposure processmay be executed by the same machine while the second exposure processmay be executed by a different machine.

Referring to FIGS. 2L and 2M, a third development process is performedto remove at least a portion of the third mask layer 600. In someembodiments, the exposure region 602 is removed such that the secondpattern P2 of the mask (not illustrated) is transferred onto the patternthird mask layer 600 a. In some embodiments, the second pattern P2 ofthe patterned third mask layer 600 a exposes at least a portion of theunderlying patterned phase shift layer 200 a.

Referring to FIGS. 2M and 2N, a third etching process is performed totransfer the second pattern P2 onto the patterned phase shift layer 200b. For example, during the third etching process, the patterned thirdmask layer 600 a and the patterned hard mask layer 300 b may be adaptedas masks such that portions of the patterned phase shift layer 200 aexposed by the second pattern P2 is removed to render the patternedphase shift layer 200 b having the second pattern P2. Since the secondpattern P2 of the patterned phase shift layer 200 b is formed byadapting the patterned hard mask layer 300 b as the mask, the contour ofthe second pattern P2 in the patterned phase shift layer 200 b and thecontour of the second pattern P2 in the patterned hard mask layer 300 bare substantially identical and are aligned. It should be noted that dueto the material difference between the hard mask layer 300 and the phaseshift layer 200, the etching recipe of the second etching process andthe third etching process may be different.

Referring to FIGS. 2N and 2O, the patterned third mask layer 600 a isremoved to obtain the photomask 10B. The patterned third mask layer 600a may be removed through, for example, a resist stripping process or aresist ashing process. In some embodiments, the steps illustrated inFIGS. 1K-1O may be collectively referred to as a third patterningprocess.

As illustrated in FIG. 2O, regions of the light transmitting substrate100 corresponding to the first pattern P1 and the second pattern P2 areexposed. Similarly, the patterned phase shift layer 200 b correspondingto the third pattern P3 is exposed. The photomask 10B has apredetermined mask pattern P which is split into a first pattern P1, asecond pattern P2, and a third pattern P3. The first pattern P1 and thethird pattern P3 are located in the first block B1 and the secondpattern P2 is located in the second block B2.

In some embodiments, the photomask 10B may be referred to as a phaseshift mask (PSM). The PSM is used to shift a phase of selected lightpassing through the mask or the reticle by π (180 degrees), thereby theundesired light is offset by the destructive interference. Removing theundesired light helps to improve the precision of the image transfer.Typically, the PSM is categorized into an attenuated PSM. In someembodiments, the photomask 10B may be referred to as an attenuated PSM.In an attenuated PSM, portions of the light transmitting substrate 100are covered by a patterned phase shift layer 200 a. A small percentage,e.g., from about 6% to about 9%, of light incident on the phase shiftlayer propagates through the phase shift layer. In some embodiments,about 12% of incident light propagates through the patterned phase shiftlayer 200 a. Regions of the light transmitting substrate 100 of theattenuated PSM which are exposed by the patterned phase shift layer 200a permit about 99% of incident light to propagate through the lighttransmitting substrate. In some embodiments where the photomask is anattenuated PSM, a thickness of the opaque layer (for example, thepatterned hard mask layer 300 b) ranges from about 5 nm to about 80 nm.A greater thickness increases absorption of incident light, therebyproviding insufficient light intensity, in some instances. However, oneof ordinary skill in the art would understand that the thickness of theopaque layer is determined by a transmission rate of the selectedmaterial and a DOF during the process. In some embodiments, based on awavelength of a light source, a thickness of the patterned phase shiftlayer 200 a ranges from about 40 nm to about 1000 nm. A greater orsmaller thickness increases a deviation from a phase shift by π,reducing a pattern resolution, in some instances. However, one ofordinary skill in the art would understand that the thickness of thephase shift layer is determined by a transmission rate of the selectedmaterial, wavelength of the light source, and a DOF during the process.For example, when the patterned phase shift layer includes molybdenumand silicon oxynitride, the thickness of the phase shifter ranges fromabout 40 nm to about 100 nm.

FIGS. 3A-3G are schematic cross-sectional views illustrating a processflow for manufacturing a photomask 10C in accordance with somealternative embodiments of the disclosure. Referring to FIG. 3A, thestep described herein is similar to the step of FIG. 1A, so the detaileddescription thereof is omitted herein. In some embodiments, a firstexposure process is performed on the first mask layer 400 within thefirst block B1 to render an exposure region 402.

Referring to FIG. 3B, a second exposure process is performed on thefirst mask layer 400 within the second block B2 to render an exposureregion 404. In some embodiments, since the precision requirements of thepatterns in the first block B1 and the second block B2 are different,the first exposure process and the second exposure process may beexecuted by different machines. For example, in some embodiments, if thepatterns in the first block B1 require higher precision (having densepitch or feature size) than the patterns in the second block B2, thefirst exposure process may be executed by a machine with higherresolution (advanced machine) while the second exposure process may beexecuted by a machine with lower resolution (lower grade machine). Insome alternative embodiments, if the patterns in the first block B1require lower precision than the patterns in the second block B2, thefirst exposure process may be executed by a machine with lowerresolution while the second exposure process may be executed by amachine with higher resolution. As such, different machines may be fullyutilized to reduce the manufacturing time by 20%-50%, thereby increasingthe throughput of the photomask.

Referring to FIGS. 3B and 3C, after the first exposure process and thesecond exposure process, a post-baking process may be performed toharden at least a portion of the first mask layer 400. Depending on thematerial(s) or type(s) of the first mask layer 400, polymers of thefirst mask layer 400 may undergo different reactions (chain scission orcross-linking of polymers) upon the irradiation of the light beam andbaking. Thereafter, a first development process is performed to removeat least a portion of the first mask layer 400. In some embodiments, thefirst mask layer 400 is made of negative tone resist material, so theexposure region 402 and the exposure region 404 are subjected to thecross-linking reaction. Referring to FIG. 3C, the first mask layer 400other than the exposure regions 402, 404 is removed such that the firstpattern P1 and the second pattern P2 of the mask (not illustrated) aretransferred onto the pattern first mask layer 400 a. In someembodiments, the first pattern P1 and the second pattern P2 of thepatterned first mask layer 400 a exposes at least a portion of theunderlying hard mask layer 300.

Referring to FIGS. 3C and 3D, a first etching process is performed totransfer the first pattern P1 and the second pattern P2 onto thepatterned hard mask layer 300 a. For example, during the first etchingprocess, the patterned first mask layer 400 a may be adapted as a masksuch that portions of the hard mask layer 300 exposed by the firstpattern P1 and the second pattern P2 is removed to render the patternedhard mask layer 300 a having the first pattern P1 and the second patternP2. In some embodiments, the first pattern P1 and the second pattern P2of the patterned hard mask layer 300 a exposes at least a portion of theunderlying phase shift layer 200.

Referring to FIGS. 3D and 3E, the patterned first mask layer 400 a isremoved. The patterned first mask layer 400 a may be removed through,for example, a resist stripping process or a resist ashing process.After the patterned first mask layer 400 a is removed, the structureillustrated in FIG. 3E may further undergo an inspection process and acleaning process. During the inspection process, the first pattern P1and the second pattern P2 are inspected to ensure that the contour ofthe first pattern P1 and the second pattern P2 are in accordance withthe desired pattern (the pattern of the mask provided initially).

Referring to FIGS. 3E and 3F, a second etching process is performed totransfer the first pattern P1 and the second pattern P2 onto thepatterned phase shift layer 200 a. For example, during the secondetching process, the patterned hard mask layer 300 a may be adapted as amask such that portions of the phase shift layer 200 exposed by thefirst pattern P1 and the second pattern P2 is removed to render thepatterned phase shift layer 200 a having the first pattern P1 and thesecond pattern P2. Since the first pattern P1 of the patterned phaseshift layer 200 a is formed by adapting the patterned hard mask layer300 a as the mask, the contour of the first pattern P1 in the patternedphase shift layer 200 a and the contour of the first pattern P1 in thepatterned hard mask layer 300 a are substantially identical and arealigned. Similarly, the contour of the second pattern P2 in thepatterned phase shift layer 200 a and the contour of the second patternP2 in the patterned hard mask layer 300 a are substantially identicaland are aligned. It should be noted that due to the material differencebetween the hard mask layer 300 and the phase shift layer 200, theetching recipe of the first etching process and the second etchingprocess may be different.

Referring to FIGS. 3F and 3G, the patterned hard mask layer 300 a isremoved to obtain the photomask 10C. As illustrated in FIG. 3G, afterthe patterned hard mask layer 300 a is removed, regions of the lighttransmitting substrate 100 corresponding to the first pattern P1 and thesecond pattern P2 are exposed by the patterned phase shift layer 200 a.The photomask 10C has a predetermined mask pattern P which is split intoa first pattern P1 and a second pattern P2. The first pattern P1 islocated in the first block B1 and the second pattern P2 is located inthe second block B2. In some embodiments, the photomask 10C may bereferred to as a super binary mask (SBIM).

It should be noted that FIGS. 3A-3G presented above mainly focus on theformation of patterns. Optionally, in some embodiments, a plurality ofmarks (alignment marks) are also formed at the same time as the firstpattern P1 and the second pattern P2 are formed. The detaileddescriptions with respect to alignment mark is presented herein. FIG. 5Ais a schematic top view illustrating a first mask layer 400 during thefirst exposure process in FIG. 3A. FIG. 5B is a schematic top viewillustrating a first mask layer 400 during the second exposure processin FIG. 3B.

Referring to FIG. 5A, during the first exposure process as described inFIG. 3A, a plurality of first marks AM1 are formed in the first masklayer 400. In some embodiments, the first marks AM1 are formed at thecorner of the first mask layer 400. In some alternative embodiments, thefirst marks AM1 are formed at the edge region of the first mask layer400. The positions of the first marks AM1 are not particularly limitedas long as the first marks AM1 do not disrupt the first patterns P1 andthe second patterns P2. Referring to FIG. 5B, during the second exposureprocess as described in FIG. 3B, a plurality of second marks AM2 arealso formed in the second mask layer 400. In some embodiments, thesecond marks AM2 are desired to be formed at the same positions as thatof the first marks AM1. In some embodiments, the second marks AM2 areformed at the corner of the second mask layer 500. In some alternativeembodiments, the second marks AM2 are formed at the edge region of thesecond mask layer 500.

Subsequently, during the first development process as described in FIG.3C, the first marks AM1 and the second marks AM2 are transferred ontothe patterned first mask layer 400. Thereafter, during the steps ofFIGS. 3D-3F, the first marks AM1 and the second marks AM2 aretransferred onto the patterned phase shift layer 200 a and the patternedhard mask layer 300 a based on the same manner as that of the firstpattern P1 and the second pattern P2. In other words, the first marksAM1 and the second marks AM2 are located at corners or edge regions ofthe patterned phase shift layer 200 a and the patterned hard mask layer300 a. It should be noted that the first marks AM1 and the second marksAM2 are not illustrated in FIGS. 3A-3F since the cross-sectional linedoes not pass through the positions where the first marks AM1 and thesecond marks AM2 are located. Moreover, although FIG. 5A illustratedthree first marks AM1 and FIG. 5B illustrated three second marks AM2,the number of the first marks AM1 and the second marks AM2 is notlimited thereto. In some alternative embodiments, more or less firstmarks AM1 and second marks AM2 may be formed during the first exposureprocess and the second exposure process.

Ideally, after the photomask 10C is obtained, a number of the firstmarks AM1 should be the same as a number of the second marks. Meanwhile,the first marks AM1 and the second marks AM2 should completely overlapwith each other in a thickness direction (z-direction). However, in someembodiments, due to errors of the machinery, the first marks AM1 and thesecond marks AM2 may not necessarily completely overlap with each otheror may not necessarily have the same number. Under this scenario, arunout (ASI/Runout) process is performed after the photomask 10C isobtained. For example, the ASI/Runout process may be performed tocalculate a deviation between the first exposure process and the secondexposure process based on a distance between each of the first marks AM1and each of the second marks AM2. During the ASI/Runout process, if thedistance is within a set range, the predetermined mask pattern P isindicated as aligned. On the other hand, if the distance is not withinthe set range, the predetermined mask pattern P is indicated asmisaligned. It should be noted that the term “aligned” and the term“misaligned” is referring to the relationship between the predeterminedmask pattern P obtained and the pattern on the mask initially providedfor manufacturing the photomask 10C. In some embodiments, the set rangemay be 300 μm in both the x-direction and the y-direction. In someembodiments, as compared to the conventional alignment marks, a numberof the first marks AM1 and the second marks AM2 may be reduced. Forexample, unnecessary alignment marks in the conventional photomask notbeing used by the exposure machines may be omitted in the disclosure. Assuch, the throughput of the photomask may be further enhanced.

In some embodiments, in order to prevent the mismatch patterning thatexisted inherently due to variation between each machines (for example,the machine performing the first exposure process and the machineperforming the second exposure process), a buffer block may be presentedto surround the blocks in which lower resolution patterns are formed.FIG. 5C is a schematic top view illustrating a portion of a photomask.Referring to FIG. 5C, the photomask is divided into a first block B1, asecond block B2, and a third block B3. The second block B2 surrounds thefirst block B1 and the third block B3 surrounds the second block B2. Insome embodiments, the first block B1 may include high resolutionpatterns. On the other hand, the second block B2 and the third block B3may include low resolution patterns. In order to prevent mismatch inpatterning, the photomask may further include first buffer blocks BB1and second buffer blocks BB2. The first buffer blocks BB1 surround thesecond block B2 and the second buffer blocks BB2 surround the thirdblock B3. Each first buffer block BB1 may have a width of 300 μm. Inother words, the first buffer blocks BB1 on both sides of the secondblock B2 may have a total width of 600 μm. Similarly, each second bufferblock BB2 may have a width of 300 μm, and the second buffer blocks BB2on both sides of the third block B3 may have a total width of 600 μm. Insome embodiments, in order to avoid light leakage at the edges of thepredetermined pattern P due to misalignment, the first buffer blocks BB1and the second buffer blocks BB2 may be subjected to exposure such thatthe predetermined pattern P is formed within the region bounded by thefirst buffer blocks BB1 and within the region bounded by the secondbuffer blocks BB2. With the addition of the first buffer block BB1 andthe second buffer block BB2, the mismatch pattering due to variationbetween each machines may be sufficiently alleviated.

It should be noted that in FIGS. 5A-5B, the first marks AM1 and thesecond marks AM2 are respectively formed in conjunction with the firstexposure process and the second exposure process. However, thedisclosure is not limited thereto. In some alternative embodiments, themarks AM may be formed prior to the first exposure process. FIG. 6 is aschematic top view illustrating a first mask layer 400 in FIG. 3A inaccordance with some alternative embodiments. Referring to FIG. 6,before the first exposure process, the marks AM may be formed at cornersof the first mask layer 400. During the steps as illustrated in FIGS.3A-3G, the marks AM may be transferred onto corners of the patternedhard mask layer 300 b and corners of the patterned phase shift layer 200b while serving the function of aiding alignment.

It should be noted that the content with respect to the first marks AM1,the second marks AM2, and the marks AM described above utilizesembodiments adapting negative tone photoresist as examples, but thedisclosure is not limited thereto. The foregoing contents may also applyto embodiments adapting positive tone photoresist (for example, theembodiments of FIGS. 1A-1L and FIGS. 2A-2O).

FIGS. 4A-4K are schematic cross-sectional views illustrating a processflow for manufacturing a photomask 10D in accordance with somealternative embodiments of the disclosure. Referring to FIGS. 4A-4F, thesteps described herein is similar to the steps of FIGS. 3A-3F, so thedetailed description thereof is omitted herein. In some embodiments, thefirst pattern P1 is located between the exposure regions 402, 404, asillustrated in FIG. 4C.

Referring to FIG. 4G, a second mask layer 500 is formed on the patternedhard mask layer 300 a. A material and a formation method of the secondmask layer 500 may be similar to the first mask layer 400, so thedetailed description thereof is omitted herein.

Referring to FIG. 4H, a third exposure process is performed on thesecond mask layer 500. The third exposure process may be similar to thefirst exposure process and the second exposure process, so the detaileddescription thereof is omitted herein. In some embodiments, the thirdexposure process is performed by irradiating a light beam onto at leasta portion of the second mask layer 500 to form an exposure region 502.In some embodiments, the exposure region 502 is located in the firstblock B1. In other words, the third exposure process is performed on thefirst block B1. In some embodiments, the exposure region 502 is formedto be partially overlapped with the first pattern P1. In someembodiments, the first exposure process, the second exposure process,and the third exposure process may be executed by different machines.However, the disclosure is not limited thereto. In some alternativeembodiments, the first exposure process and the third exposure processmay be executed by the same machine while the second exposure processmay be executed by a different machine.

Referring to FIGS. 4H and 4I, a second development process is performedto remove at least a portion of the second mask layer 500. In someembodiments, the exposure region 502 is removed such that the thirdpattern P3 of the mask (not illustrated) is transferred onto the patternsecond mask layer 500 a. In some embodiments, the third pattern P3 ofthe patterned second mask layer 500 a exposes at least a portion of theunderlying patterned hard mask layer 300 a. In some embodiments, thethird pattern P3 of the patterned second mask layer 500 a is partiallyoverlap with the first pattern P1. In other words, the third pattern P3also exposes the first pattern P1.

Referring to FIGS. 4I and 4J, a third etching process is performed totransfer the third pattern P3 onto the patterned hard mask layer 300 b.For example, during the third etching process, the patterned second masklayer 500 a may be adapted as a mask such that portions of the patternedhard mask layer 300 a exposed by the third pattern P3 is removed torender the patterned hard mask layer 300 b having the third pattern P3.In some embodiments, the third pattern P3 of the patterned hard masklayer 300 b exposes at least a portion of the underlying patterned phaseshift layer 200 a. In addition, the third pattern P3 exposes the firstpattern P1 and a portion of the light transmitting substrate 100.

Referring to FIGS. 4J and 4K, the patterned second mask layer 500 a isremoved to obtain the photomask 10D. The patterned second mask layer 500a may be removed through, for example, a resist stripping process or aresist ashing process. As illustrated in FIG. 4K, regions of the lighttransmitting substrate 100 corresponding to the first pattern P1 and thesecond pattern P2 are exposed, and the patterned phase shift layer 200 acorresponding to the third pattern P3 is exposed. The photomask 10D hasa predetermined mask pattern P which is split into a first pattern P1, asecond pattern P2, and a third pattern P3. The first pattern P1 and thethird pattern P3 are located in the first block B1 and the secondpattern P2 is located in the second block B2. In some embodiments, thephotomask 10D may be referred to as an attenuated PSM.

It should be noted that the foregoing discussion mainly focuses on themanufacturing method of a photomask. However, the disclosure is notlimited thereto. In some alternative embodiments, the methods presentedin FIGS. 1A-1L, 2A-2O, 3A-3G, 4A-4K, 5A-5C, and 6 may also apply to aphotolithography process for patterning a wafer (a wafer writingprocess). In addition, although the first pattern P1 and the secondpattern P2 in FIGS. 1A-1L, 2A-2O, 3A-3G, 4A-4K are represented byopenings, the disclosure is not limited thereto. In some alternativeembodiments, the first pattern P1 and the second pattern P2 may alsorefer to traces, blocks, or lines formed on the photomask 10A, 10B, 10C,and 10D.

In accordance with some embodiments of the disclosure, a method ofmanufacturing a photomask includes at least the following steps. First,a phase shift layer and a hard mask layer are formed on a lighttransmitting substrate. A predetermined mask pattern is split into afirst pattern and a second pattern. A series of processes is performedso that the hard mask layer and the phase shift layer have the firstpattern and the second pattern. The series of processes includes atleast the following steps. First, a first exposure process fortransferring the first pattern is performed. Thereafter, a secondexposure process for transferring the second pattern is performed. Thefirst exposure process and the second exposure process are executed bydifferent machines.

In accordance with some alternative embodiments of the disclosure, amethod of manufacturing a photomask includes at least the followingsteps. First, a phase shift layer and a hard mask layer are formed on alight transmitting substrate. A predetermined mask pattern is split intoa first pattern, a second pattern, and a third pattern. A firstpatterning process is performed so that the hard mask layer has thefirst pattern. A first etching process is performed using the hard masklayer as a mask, so that the phase shift layer has the first pattern. Asecond patterning process is performed so that the hard mask layer hasthe second pattern and the third pattern. A third patterning process isperformed so that the phase shift layer further has the second pattern.

In accordance with some embodiments of the disclosure, a photomaskincludes a light transmitting substrate and a phase shift layer. Theshift layer is disposed on the light transmitting substrate. The phaseshift layer has at least one first mark.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method of manufacturing a photomask,comprising: forming a phase shift layer and a hard mask layer on a lighttransmitting substrate; splitting a predetermined mask pattern into afirst pattern, a second pattern, and a third pattern; performing a firstpatterning process using a first photoresist layer so that the hard masklayer has the first pattern; removing the first photoresist layer;performing a first etching process using the hard mask layer as a mask,so that the phase shift layer has the first pattern; performing a secondpatterning process using a second photoresist layer so that the hardmask layer has the second pattern and the third pattern; removing thesecond photoresist layer; performing a third patterning process using athird photoresist layer so that the phase shift layer further has onlythe second pattern, wherein the second pattern does not overlap with thefirst pattern, and the third pattern partially overlaps with the firstpattern; and removing the third photoresist layer.
 2. The method ofclaim 1, wherein the hard mask layer is an opaque layer, regions of thelight transmitting substrate corresponding to the first pattern and thesecond pattern are exposed, and the phase shift layer corresponding tothe third pattern is exposed.
 3. The method of claim 1, wherein thefirst patterning process comprises a first exposure process, the secondpatterning process comprises a second exposure process, the thirdpatterning process comprises a third exposure process, and the firstexposure process, the second exposure process, and the third exposureprocess are executed by different machines having different resolutions.4. The method of claim 1, wherein the second pattern and the thirdpattern of the hard mask layer expose at least a portion of the phaseshift layer.
 5. A method of manufacturing a photomask, comprising:sequentially forming a phase shift layer, a hard mask layer, and a firstmask layer on a light transmitting substrate; performing a firstexposure process and a first development process to form a first patternin the first mask layer; transferring the first pattern into the hardmask layer and the phase shift layer to form a patterned hard mask layerand a patterned phase shift layer; removing the first mask layer;forming a second mask layer on the patterned hard mask layer; performinga second exposure process and a second development process to form asecond pattern and a third pattern in the second mask layer;transferring the second pattern and the third pattern into the patternedhard mask layer; removing the second mask layer; forming a third masklayer on the patterned hard mask layer and the patterned phase shiftlayer; performing a third exposure process and a third developmentprocess to form only the second pattern in the third mask layer;transferring the second pattern in the third mask layer into thepatterned phase shift layer, wherein the second pattern does not overlapwith the first pattern, and the third pattern partially overlaps withthe first pattern; and removing the third mask layer.
 6. The method ofclaim 5, wherein the patterned hard mask layer is an opaque layer,regions of the light transmitting substrate corresponding to the firstpattern and the second pattern are exposed, and the patterned phaseshift layer corresponding to the third pattern is exposed.
 7. The methodof claim 5, wherein the first mask layer, the second mask layer, and thethird mask layer are positive tone photoresists.
 8. The method of claim5, wherein the step of transferring the second pattern and the thirdpattern into the patterned hard mask layer comprises: performing anetching process to remove the patterned hard mask layer exposed by thesecond pattern and the third pattern using the second mask layer as amask.
 9. The method of claim 5, wherein the first exposure process, thesecond exposure process, and the third exposure process are executed bydifferent machines having different resolutions.
 10. The method of claim5, wherein the second pattern and the third pattern of the patternedhard mask layer expose at least a portion of the patterned phase shiftlayer.
 11. A method of manufacturing a photomask, comprising:sequentially forming a phase shift layer, a hard mask layer, and a firstphotoresist layer having a first pattern on a light transmittingsubstrate; transferring the first pattern in the first photoresist layerinto the hard mask layer to form a patterned hard mask layer; removingthe first photoresist layer; transferring the first pattern in thepatterned hard mask layer into the phase shift layer to form a patternedphase shift layer; forming a second photoresist layer having a secondpattern and a third pattern on the patterned hard mask layer;transferring the second pattern and the third pattern into the patternedhard mask layer; removing the second photoresist layer; forming a thirdphotoresist layer having only the second pattern on the patterned hardmask layer and the patterned phase shift layer; transferring the secondpattern in the third photoresist layer into the patterned phase shiftlayer, wherein the second pattern does not overlap with the firstpattern, and the third pattern partially overlaps with the firstpattern; and removing the third photoresist layer.
 12. The method ofclaim 11, wherein the patterned hard mask layer is an opaque layer,regions of the light transmitting substrate corresponding to the firstpattern and the second pattern are exposed, and the patterned phaseshift layer corresponding to the third pattern is exposed.
 13. Themethod of claim 11, wherein the first photoresist layer, the secondphotoresist layer, and the third photoresist layer are positive tonephotoresists.
 14. The method of claim 11, wherein the step oftransferring the second pattern and the third pattern into the patternedhard mask layer comprises: performing an first etching process to removethe patterned hard mask layer exposed by the second pattern and thethird pattern using the second photoresist layer as a mask.
 15. Themethod of claim 14, wherein the step of transferring the second patternin the third photoresist layer into the patterned phase shift layercomprises: performing an second etching process to remove the patternedphase shift layer exposed by the second pattern using the thirdphotoresist layer as a mask.
 16. The method of claim 15, wherein anetching recipe of the first etching process and an etching recipe of thesecond etching process are different.
 17. The method of claim 11,wherein the third photoresist layer covers the third pattern of thepatterned hard mask layer and the first pattern of the phase shiftlayer.
 18. The method of claim 11, wherein the step of transferring thefirst pattern in the first photoresist layer into the hard mask layer toform the patterned hard mask layer comprises: performing an etchingprocess to remove the hard mask layer exposed by the first pattern usingthe first photoresist layer as a mask.
 19. The method of claim 11,wherein the step of transferring the first pattern in the patterned hardmask layer into the phase shift layer to form the patterned phase shiftlayer comprises: performing an etching process to remove the phase shiftlayer exposed by the first pattern using the patterned hard mask layeras a mask.
 20. The method of claim 11, wherein the second pattern andthe third pattern of the patterned hard mask layer expose at least aportion of the patterned phase shift layer.